Petunia Flower Senescence

Abstract

Senescence represents the last stage of floral development and is an active process that requires gene transcription and protein translation. A genetically controlled senescence program allows for the ordered degradation of organelles and macromolecules and the remobilization of essential nutrients from the petals. Petunia provides an excellent model system for studies of flower senescence because the plants flower profusely and have large floral organs amenable to molecular and biochemical analysis. While Petunia flowers have a finite lifespan that is under tight developmental control, petal senescence can be accelerated and synchronized by means of exogenous ethylene or by pollination. Petal senescence in Petunia is accompanied by decreased nucleic acid and protein content, DNA and nuclear fragmentation, and structural and compositional changes in the plasma membrane. These changes are correlated with increased mRNA abundance and enzyme activity of proteases, nucleases, and phospholipases. Major macronutrient levels in Petunia petals (collectively called the corolla) also decrease during senescence. These studies support cellular degradation and remobilization as the central functions of petal senescence. Ethylene is clearly involved in modulating the process, but the transcription factors and other components of the senescence signal transduction pathway(s) remain to be elucidated. Further studies focusing on early transcriptome changes during petal senescence will help to identify these early regulators, and subsequent studies of protein changes and the post-translational modification of senescence-related proteins will further our understanding of the pathways executing the senescence program.